1. Field
The present invention relates to a seal equipped bearing assembly for use in a transmission of a type used in automotive vehicles.
2. Description of the Related Art
The transmission used in automotive vehicles generally contains foreign matter such as wear debris resulting from gears employed therein. For this reason, prior art bearing units employed in the automobile transmission are each generally employed in the form of a seal equipped bearing unit of a kind utilizing a contact type sealing member used to seal each of the opposite open ends of an annular bearing space delimited between inner and outer rings of the respective bearing unit, to thereby prevent ingress of the foreign matter into each of the bearing units.
Where the annular bearing space is sealed at its opposite open ends with the respective contact type sealing members, an undesirable ingress of the foreign matter can be successfully prevented, but the sealing torque (i.e., the torque, which tends to occur when each of the sealing members slidingly contacts the bearing rotatable ring and which constitutes a resistance to the rotation of the bearing unit) is considerably high enough to bring about a mechanical loss of the driving torque, and this tends to pose a problem in reduction in fuel consumption of the automotive vehicle.
In the seal equipped bearing unit of the kind discussed above, it has been suggested to reduce the sealing torque (in, for example, Japanese Patent Publication No. 2007-107588 discussed below) by effecting a shot peening a surface of one or more sealing lips of each of the sealing member, for example, an inner wall surface of a seal groove defined in the bearing rotatable ring, to render the contact surface to have a surface roughness not larger than 2.5 μm at the maximum height of irregularities Ry.
According to the reduction of the surface roughness of the contact surface to thereby reduce the sealing torque such as employed in the seal equipped bearing unit disclosed in Japanese Patent Publication No. 2007-107588, the extent to which the torque is reduced is limited and no satisfactory effect of reducing the torque can be obtained. Although the use of a non-contact seal will be effective to reduce the sealing torque to zero, reduction in size of the seal gap to such an extent that the undesirable ingress of the foreign matter such as, for example, wear debris resulting from the transmission gears can be prevented will be difficult to achieve because of an error in assemblage, an error in processing, difference in thermal expansion and some other factors.